November modeled soil moisture indicated much below and below average conditions for most of Green River Basin. (Click for November 1st image) This signal is incorporated in the ESP model guidance utilized by the CBRFC to generate forecasts. At the time of this publication, seasonal precipitation is near normal for most of the region. However, April precipitation was much above average in the Upper Green, Duchense, and Lower Green river basins. Snowpack is past the seasonal peaks. Median April water supply forecasts increased in the Upper Green, Duchense, and Lower Green river basins and dropped slighty in the Yampa/White river basin.

-Model Soil Moisture/Observed Streamflow...The November soil moisture conditions were much below average in the Upper Green River basin. Observed streamflow for the month of April was 80 percent of average.

-Snowpack/Precipitation...In the Upper Green River basin, April precipitation was 155 percent of average. On May 1st, the basinwide snowpack was 95 percent of average.

-General Discussion...Weather models suggest no precipitation for the the next 5 days, and slightly above normal precipitation for the following 6-10 day period. Beyond that the 30 Day CPC guidance shows below average precipitation as likely. April through July guidance indicate below average to near average runoff volumes for points above Flaming Gorge.

-Model Soil Moisture/Observed Streamflow...Fall soil moisture estimates were near average in the headwaters of the Yampa and White River basin. Soil moisture deficits are not adversely effecting model guidance as much as in other regions. Observed streamflow for the month of April was 125 precent of average.

-Snowpack/Precipitation...On May 1st, the basinwide snowpack was 95 percent of average. April precipitation was 115 precent of average.

-General Discussion...Weather models suggest no precipitation for the the next 5 days, and normal precipitation for the following 6-10 day period. Beyond that the 30 Day CPC guidance shows equal chances for above, normal, or below average precipitation. April through July guidance indicate runoff volumes from average to much above average for the Yampa and White River basin.

-Model Soil Moisture/Observed Streamflow...Fall soil conditions in the Duchesne were similar to the Upper Green with many basins indicating much below average conditions. Observed streamflow for the month of April was average.

-Snowpack/Precipitation...The snowpack in the Duchesne River basin on May 1st was 75 percent of average. April precipitation was 170 percent of average.

-General Discussion...Weather models suggest no precipitation for the the next 5 days, and slightly above normal precipitation for the following 6-10 day period. Beyond that the 30 Day CPC guidance shows below average precipitation as likely. Forecasts range from average in the headwaters of the basin to below average at downstream locations.

-Model Soil Moisture/Observed Streamflow...The November soil moisture conditions were much below average in the Lower Green River basin and continues to drive lower model guidance. Observed streamflows for the months of February, March, and April were below average.

-Snowpack/Precipitation...The Lower Green River basin snowpack was 55 percent of average on May 1st. April precipitation was 155 percent of average.

-General Discussion...Weather models suggest no precipitation for the the next 5 days, and slightly above normal precipitation for the following 6-10 day period. Beyond that the 30 Day CPC guidance shows below average precipitation as likely. Forecasts range from below average to near average with the exception of Ferron Creek forecasted at much below average.

Differences between the full period forecasts and the residual forecasts may not exactly equal the actual observed volumes due to rounding conventions (see Definitions section).

10% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 10% chance of being exceeded. Previously referred to as "Reasonable Maximum Forecast".

50% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 50% chance of being exceeded. Previously referred to as "Most Probable Forecast".

90% exceedance forecast: Given the current hydrometeorological conditions, i.e current snowpack, soil moisture and streamflow, the volume that has a 90% chance of being exceeded. Previously referred to as "Reasonable Minimum Forecast".

Acre-Foot (af): The volume equal to one acre covered one foot deep (43,560 cubic feet). See kaf below.

Average: The arithmetic mean. The sum of the values divided by the number of values. Values from 1971-2000 are used for this publication.

Categories: Much Above Average=Greater than 130%, Above Average=111-130%, Near Average=90-110%, Below Average=70-89%, Much Below Average=Less than 70%.

CBRFC: Colorado Basin River Forecast Center.

Forecast Period: The period from April 1 through July 31, unless otherwise noted.

kaf: Thousand Acre-Feet. See Acre-Foot above.

Inflow: The volume of water that flows into a reservoir or lake.

Median: The middle value of an ordered set of values. Half of the values are higher and half of the values are lower. When the set contains an even number of values the median is the average of the two middle numbers.

NOAA: National Oceanic and Atomospheric Administration.

NWS: National Weather Service.

Water supply forecasts take into consideration present hydrometeorological conditions and use average basin temperatures and precipitation for the forecast period. As the forecast season progresses, a greater portion of the future hydrologic and climatic uncertainty becomes known and monthly forecasts become more accurate. For more information on the tools we use, consult Water Supply Forecasting Tools.

Volume forecasts represent adjusted flows; that is, observed flows with upstream water use taken into account. Adjusted flows will closely approximate natural or unimpaired flows. However, not all upstream diversions or impoundments are measured or quantifiable. For specific adjustments used with each forecast point, consult the Guide to Water Supply Forecasting.

The Water Supply Outlook is issued monthly January through May by the Colorado Basin River Forecast Center. It represents a coordinated effort between the National Weather Service, Natural Resources Conservation Service, Bureau of Reclamation, U.S. Geological Survey and local water district managers.

Note: Data used in this report are provisional and are subject to revision.

For more information, or to be included on the mailing list, please contact:

Colorado Basin River Forecast Center
2242 W North Temple
Salt Lake City, UT 84116
(801) 524-5130
www.cbrfc.noaa.gov